Reliability is an important evaluating indicator of the quality of a semiconductor chip, especially, a memory chip with high density. In general, a failure rate of a lot of memory chips must be less than a predetermined vale required by a custom, for example, 32 defects parts per million (DPPM). The failure rate of the memory chips is less, and the reliability of the memory chips is better. However, in a conventional method for evaluating failure rate, each of the memory chips is used as an evaluating unit. Thus, a huge amount of the memory chips are used as samples to be tested. For example, if the failure rate of the memory chips is required to be equal to 32 DPPM, more than 4000 memory chips are generally provided to be tested so as to evaluate the exact failure rate of the memory chips. Thus, the conventional method for evaluating the failure rate includes a time-consuming and laborious testing process, which has a high evaluating cost.
Therefore, what is needed is to a method for evaluating failure rate to overcome the above disadvantages.